One of the problems that plagues advanced control strategies and attempts to maintain stable process operating temperatures in various operating processes in the chemical, petrochemical, and allied industries is the inability to cope with severe environmental changes (i.e., rain storms). Existing feedforward methods and multi-variable control technologies attempt to compensate for all of the process disturbances (i.e., feedstock changes, mass flow changes, etc.) and are effective in coping with these demands. Feedforward methods are defined as the anticipation of a required action to prevent an error or a condition from causing an undesired effect. These controllers may include ambient temperature as a disturbance feedforward variable, however ambient temperature alone does not reflect the full environmental thermal impact on operating processes. Ambient temperature is defined as the free air temperature unaffected by conditions such as sunlight, wind, or precipitation.
The large change in heat flux (defined herein as the amount of calories that are input or output to/from a process unit over a period of time) due to rain storms and/or other factors such as wind or radiation, acts to blindside process controllers since no disturbance variables are included in their cascade (control) strategy or in the multi-variable controller matrix. Many operating processes in the chemical, petrochemical, and allied industries currently experience pronounced undesirable effects on fractionators, reactors etc. from these types of environmental impacts.
The prior art does not address such environmental thermal impact on operating processes. U.S. Pat. Nos. 4,030,986, 4,620,284, 5,260,865, 4,616,325, 4,630,221, 4,672,842, 4,821,524, 5,150,690, and 5,139,548 all fail to even recognize the need to compensate for such environmental affects.
In order to provide feedforward control techniques to compensate for these types of environmental impact, Applicants hereby disclose the use of contemporary meteorological indicators (i.e., ambient temperature, rate of rain fall, radiometry input, wind speed, etc.) to compensate for ambient environmental process loading. While these indicators are beneficial as process feedforward inputs, their relationship is not straight forward and several pieces of instrumentation and complex mathematical solutions are required to fully compensate for these multiple environmental effects.
The prior art does not teach any means for evaluating the effects of such environmental factors on such industrial operating processes in a manner that could be used for feedforward controlling techniques.
It is therefor desirable to provide a simple, accurate, and economical feedforward compensation measurement method and apparatus that are directly related to the environmental BTU loading of these combined environmental effects. Applicants have developed an instrument and procedure which measures the combined effect of these variables directly. An accurate measurement is obtained by maintaining a physical test element at an arbitrary fixed temperature differential from ambient temperature, by means of a differential temperature controller, wherein the power (watts) required to maintain this differential temperature is representative of the BTU loading as a result of the aforementioned environmental conditions. In the preferred embodiment, a single apparatus can effectively provide feedforward compensation to several processing units.